The majority of present day integrated circuits (ICs) are implemented by using a plurality of interconnected field effect transistors (FETs), also called metal oxide semiconductor field effect transistors (MOSFETs), or simply MOS transistors. An MOS transistor includes a gate electrode as a control electrode and spaced apart source and drain electrodes between which a current can flow. A control voltage applied to the gate electrode controls the flow of current through a channel between the source and drain electrodes.
MOS transistors, in contrast to bipolar transistor, are majority carrier devices. The gain of an MOS transistor, usually defined by the transconductance (gm), is proportional to the mobility of the majority carrier in the transistor channel. The current carrying capability and hence the performance of an MOS transistor is proportional to the mobility of the majority carrier in the channel. The mobility of holes, the majority carrier in a P-channel MOS transistor can be increased by applying a compressive longitudinal stress to the channel. The mobility of electrons, the majority carrier in an N-channel MOS transistor, however, is decreased by such a compressive longitudinal stress to the channel. To increase the mobility of electrons, a tensile transverse stress must be applied to the channel of the MOS transistor.
Accordingly, it is desirable to provide methods for fabricating MOS transistors that improves the mobility of both P-channel and N-channel MOS transistors. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.